The present invention relates to systems and methods for applying a thin coat of a substance such as a lubricant, protective, decorative, optical (e.g., filter) or other coating to a substrate, and more particularly to systems and methods for applying such coats to a single side only of a substrate, object or material utilizing a solvent bath containing a concentration of the coating material.
Proper application of a thin layer of a substance such as a lubricant or protective film onto a substrate is generally one of the most critical considerations in processes involving the manufacture of items such as magnetic hard discs, semiconductor devices, circuit boards, flat panels such as liquid crystal displays, optical components such as mirrors, lenses, gratings and optical filters, etc. The coating layer must often have a precise and uniform thickness or the functional characteristics of the substrate are adversely affected. Moreover, the coating may have a thickness requirement that is so thin as to be difficult to obtain using generally known processes.
Often times available processes envision coating of both sides of a substrate, coating on only one side being impractical in view of the process. One process used for applying coating to one side of a substrate is called spin coating. In this process a substrate is spun about a rotation axis and a mixture of solvent and the coating material is poured onto the spinning substrate. The thickness of the coating is controlled by controlling the angular velocity of the spinning substrate and the viscosity of the mixture of solvent and coating material. Coatings applied with the spin process are often difficult to control in thickness and generally result in a greater thickness near the outer edges of the spinning substrate.
A process for providing coating thicknesses under one thousand Angstroms together with an apparatus for performing such processes to one side only of a substrate is needed throughout those industries that require ultra thin and precise coating applications.
In one aspect of the invention, an apparatus is provided for applying a thin coat of a substance to a substrate, wherein a predetermined concentration of the substance is mixed with a solvent to formulate a solvent bath. Further, the thin coat is applied to one substantially planar side of the substrate. The apparatus includes means for containing the solvent bath so that a bath surface on the solvent bath is substantially free of disturbance. Means is also provided for positioning the one substantially planar side in contact with the bath surface. In addition, means is provided for tilting the one substantially planar side to assume a predetermined angle with respect to the bath surface while remaining in contact therewith. Means is provided for separating the one substantially planar side from the bath surface so that a meniscus therebetween travels across the one substantially planar side at a predetermined speed.
In another aspect of the invention, an apparatus is provided for applying a thin coat of a substance to one planar side of a substrate, wherein the substance is mixed in a predetermined concentration with a solvent in a solvent bath having a substantially undisturbed bath surface thereon. The apparatus includes a bath container and means for positioning the one planar side of the substrate in contact with the substantially undisturbed bath surface. The means for positioning operates to orient the one planar side at a predetermined angle relative to the substantially undisturbed bath surface. Means is also provided for separating the one planar side from the substantially undisturbed bath surface, whereby a meniscus extends across and between the one planar side only and the substantially undisturbed bath surface. Further, means is provided that operates in conjunction with the means for separating for controlling a speed of traversal of the meniscus across the one planar side, wherein the speed of traversal corresponds substantially to an evaporation rate of the solvent in the solvent bath.
In yet another aspect of the invention, an apparatus is provided for applying coat in as of less than one thousand Angstroms thick on one side of a substrate having an area for coating defined by continuous substrate edges. The coating substance is carried in a solvent, thereby providing a predetermined concentration of a coating substance in a solvent mix. The apparatus includes a solvent mix container for holding a quantity of solvent mix, so that the solvent mix has a substantially undisturbed free surface. Further. means is provided for positioning the one side in contact with the substantially undisturbed free surface at an angle thereto, and forming a meniscus adjacent one of the continuous substrate edges. Means is present for separating the one side and the substantially undisturbed free surface to provide a meniscus speed of traversal across the one side that corresponds to the evaporation rate of the solvent. In this fashion the one side is substantially free of solvent immediately following passage of the meniscus.
In still another aspect of the invention, a method is disclosed for applying a thin coat of a substance onto one side of a substrate. The method includes the steps of mixing the substance in a solvent to provide a predetermined concentration of the substance in a solvent mix. The method further includes the step of placing an amount of the solvent mix in a container so that the solvent mix has an accessible undisturbed free surface. Additionally, the method includes the step of positioning the one side in contact with and at a predetermined angle to the accessible undisturbed free surface. A meniscus is formed in the solvent mix extending between the undisturbed free surface and the one side. The process proceeds by separating the one side and the solvent mix at a separation rate so that the meniscus traverses the one side at a rate corresponding to a solvent evaporation rate.
Accordingly, it is an object of the present invention to provide systems and methods for coating one side of a substrate or object in which a meniscus is formed between the substrate or object and a surface of a fluid containing a coating material.
It is another object of the present invention to provide such systems and methods in which the one side of the substrate or object is positioned at a predetermined angle with respect to the surface of the fluid containing the coating material, and the one side and the surface of the fluid move relative to each other such that the meniscus travels across the surface.
It is yet another object of the present invention to provide such systems and methods in which the relative movement between the one side and the surface is substantially not uniform, and the rate of meniscus travel is substantially uniform.
Finally, it is an object of the present invention to provide such systems and methods in which the coating thickness is substantially uniform or of other desired characteristic(s), such as having a thickness below about 1000 Angstroms, and below about 900, 800, 500, 200, 100 and even about 10-20 Angstroms (e.g. lubricant films of 10-20 Angstroms. etc.).